Temperature compensator



-Z'lne 3, 1930. J. zUBATY 1,761,951

TEMPERATURE COMPENATOR Filed April 8. 1927 unita Patented .Hase 3, 193e *stares PATEa'r orrlcs JosnPHzUBA'rY, on' ELINT, MrcnrGAN, AssrGNon To A c srAnK PLUG COMPANY, vor* FLINfr, MICHIGAN, A COMPANY or MroHIGAN i TEMPERATURE ooMPENsA'ron Application inea Aprn s,

rlhis invention relates to magnetic measuring instruments, in particular to speedometers used on vehicles to indicate the rate of travel. It is well-known that errors occur in the readings of such instruments owing totemperature changes. This is due to the fact thatv at low temperatures the resistance of the .speed cup is vlow andl that the eddy currents set up in the rim of the cup are quite large, with the result that the speed indications are larger than the true value. As temperature increases the reverse action takes place until at high temperatures the indications of speed i magnetic field being due to inherent charac- .teristicsf of the fixed member.

will be lower than the true value. The correction of such errors has'been undertaken 'by the use of a movable magnetic mass, the position of which is controlled by a bi-metallie thermostat; v

By this invention it is intended to correct the inaccuracies in the readings of the instrument and to `render the readings correct at l.all temperatures by the use of a shunt of Varl- Vable conductivity, the shunt consisting of a fixed member associated with the magnet, the variable' effect of the shunt upon the active Figure l is a View in elevation of a formv shown by Figure 3.

Referring by reference characters to the drawing,vnumeral represents a frame carrying mounted thereon a magnet 7 .v Clamps 9 are employed to secure the magnet to the l frame. At 11 is shown a surrounding metallic casing. Rotatably mounted within the poles of the magnet is a rotor 18 driven by a flexible drive shaftr 15 in the illustrated embodiment of the invention. Figure 2 shows a drive shaft 17 for operating the flexible shaft having portions for connection with the flexible shaft 15 within the speedometei` and 1927. serial No. 182,077.

for connection with the external shaft driven by the part, the speedvef which is to be measured. It will also be seen that the shaft 17 carries a gear 18 for operating the odometer, not shown, which, as usual, is used together with the speedometer. Surrounding the rotor 13 is a speed cup 19 also located in the magnetic field between poles of magnet 7. At low temperaturesthe speed cup resistance isl low and the eddy currents set up in the rim of the speed cupl bythe lines of force between the magnet and the rotor are large, this resulting in an unduly high speedometer reading. 5The opposite condition prevails whenthe temperature is high.

Nickel copper alloy has a large magnetic permeability factor at low temperatures, which factor decreases with rising temperature. It is proposed to make use of such an alloy to off-set the errors noted above. To that end-clamps 9 hold, not` only the magnet 7, but also a plate of nickel copper alloy which is of somewhat U-shape and extends outwardly to a position adjacent the casing 11. This plate isv designated by numeral 20. Such a plate may be used adjacent one or both magnet poles.

Theresult of the use of such a platewwill be obvious. The plate in and of itself, but preferably withtheaid of the casing, constitutes a shunt, theV effect of which,.owing to the above mentioned characteristics of the alloy, is such as to correct the errors otherwise occuring in the readings of the speed cup. VThis result is accomplished without the use of movable parts as heretofore proposed, the movement of said parts'having been made sometimes manually and sometimes automatically through the instrumentality of a bi-metallic thermostat. By the simple expedient of attaching a piece of this,

nickel copper alloy I am able to render the readings of the structure correst forV all temperatures.

y Figures 3 and i1 show a different shape of` correcting plate..v The nickel copper alloy plate 21 is shaped as shown to engage the magnet 7 adjacent its pole with one face 23, another face 25 being in' position adjacentthe casing asbefore, there being an intermedi.-

ate connecting portion vkln this form itl.

may be convenient to secure the plate 21l by screwsQQ .tc the frame 5, inasmuchas the magnet holding clamp 9 engages the magnet in a way which renders it less convenient'to usetliis clamp Vfor alsoA holding the nickel copper alloyplate. The operatioiifoi the `temperature compensator is the saiiie'as in the Vform of theinventionpreviously de? scribed.

'Two kpractical embodiments' have been' shown and described. These are. the Atwo forms which l now consider'bes't, but it'will be understood that these should be "regarded-Y as illustrative, and that other forms maybe adopted to carry out the inventive idea.

YCertain characteristics` common to] these', two forms may be mentioned. t In both forinsr .there is the usual effective magnetic lield b'eltween the magnet poles. In eachcase some of the lines of force may passffrompole toY pole by way of a'shunt. This shunt might-be ran air passage,but it is preferable to 'use af n metal `casing to render the shunt more serviceable. The air gap` between each magnet pole and the casing prevents anyeXc'essive shunt action. The two airyga'ps provide very de-k rciaime f f 1. In combination, a magnet, an indicating member in'fthea'ctive lield; between the poles l of the magnet,-said indicating member havf i ingelectrical conductivity variable with'teniperature, a magnetic'shuiitjdistinct'from'the' i 'active' lield, y'there being 'an air-'gap lin sai'df shunt, and .compensating member'having magnetic permeabiity variable with;temper-ik 7 aturecliangespositioned/gin said gap of the shunt.v i 'f 2. Iiiic'oinbination,ainagnet, acasing in'-A i' closing said magnet, said magnethaving an l activeield'betweenf-its poles yand Fa Lshunt heldincluding said casing, therebeing an air gap betwe'ens'aidpoles and said casing with in said shunt, a rotary indicating member iii the active iield, said rotary indicating mem#V ber having electrical conductivity'variable j with temperature changes and a compensat@- 'ingr alloypmember having magnetic pernief ability Variable ,With temperature. .changesff said lCompensator,being located in, the shunt. y

gap. l

y In testimonyluwhereo. I aiiix my signature.

sirable positioiisfor the compensator. It is` possible to use a.. compensator inionel oiilyfA i of these gaps, or one may be used in'each gap o l according to the degree of'compensation reo quired.

Compensators made iuX transmission from the `compensator to the casing. In Figurelfthe base ofthe Ulsliaped member, and in Figure 4 the,partrepresent-A ed by numeral 25, constitute the `areas re'- lferred to. With compensators.ofk the mov i able type operated by bimetallie tliermostats., for example, the size of the compensator must l f accordingto either de-` o sign shown offer alarge area for magnetic y not/be so ygreat as to exceed the; limitsim! f example, by attaching the compensator tothe Vcasinginstead of tothe magnet orto the magnet frame, as inthe drawing.V Also,fthe o posed'by the operating thermostats'. fInthe case oftheixed compensators 'ofV the kind herein described, nosuchlimitations are ref` quired. yTheportion25,orexainplmmaybe made as large as it needsto be to properly correct Vfor errors due to temperature changes. Great accuracyY thus'becoines possible.V

In both ormstlie ycompensator is shown as positioned adjacent the magnet pole with an air gap between the compensator andthe casing', Obviously the compensatorv might be positioned to locate the gap betweenthe magnet and itself. :This might be done, Jfor compensator might be positioned:` mid-.way between the magnetand the casing, and thusV dividethe gap into two parts.l f t v Other changes will doubtless be discovered,

changes which may` be made indetail with' departing from the spirit of the inven- Y out tion.

sol 

